It is known that a certain number of inorganic materials, in particular unphosphated steel mill slags, the term "slag" also including scorias, represent very great quantities of residues of which only a slight part is used. Treatments performed so far on these residues make it possible to obtain products whose usage value is relatively slight, for example, granulates for making fill and layers of roads, and for soil improvement products.
In processes intended to obtain products of a small granulometry from molten materials such as slags, generally a dispersion of the material is fed onto a suitably cooled winged drum and a relatively intense cooling of the molten mass is assured by sprinkling water and/or jets of cold air thereon. The granulates of solidified slags have a porous, expanded structure, in particular when porophoric agents are incorporated in the molten mass.
When it is desired to obtain hard, non-porous products of compact structure, or, for example, blasting sands of great usage value, from the molten slags, it is necessary to crush and grind the materials recovered in the cooling pit. However, these operations consume a considerable amount of energy and cause an excessive wear of the equipment used because of the extreme abrasiveness of the materials.